Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.76   10.717%   $265.4551   $265.46   $265.45   $265.50  
  Purchase #2 $179.87   7.119%   $192.6749   $192.67   $192.65   $192.70  
  Purchase #3 $212.66   5.605%   $224.5796   $224.58   $224.60   $224.60  
  Purchase #4 $53.98   5.597%   $57.0013   $57.00   $57.00   $57.00  
  Purchase #5 $136.98   4.671%   $143.3783   $143.38   $143.40   $143.40  
  Purchase #6 $152.41   4.832%   $159.7745   $159.77   $159.75   $159.80  
  Purchase #7 $142.69   13.870%   $162.4811   $162.48   $162.50   $162.50  
  7 purchase totals = $1,118.35       $1,205.3448   $1,205.34   $1,205.35   $1,205.50